Image forming apparatuses typically include a development device to develop latent images formed on a latent image bearer (e.g., a photoreceptor) with developer, and two-component developer consisting essentially of toner (toner particles) and magnetic carrier (carrier particles) is widely used. The development device typically includes a development roller serving as a developer bearer and a developer conveyance member to transport the developer inside the development device. The developer bearer has multiple magnetic poles provided thereinside to carry developer on a rotary surface thereof (i.e., sleeve) and supplies toner included in the developer to a development range facing the latent image bearer, thereby developing the latent image formed on the latent image bearer. Additionally, such development devices typically include multiple developer conveyance members to transport developer in parallel to the rotary shaft of the developer bearer. While being circulated inside the development device, developer is supplied to the developer bearer and then collected from the developer bearer downstream from the development range in the direction of rotation of the developer bearer. In response to the amount of toner consumed in the development range, toner is supplied through a toner supply inlet to the development device and mixed with the exiting developer.
For example, JP-2010-197539-A and JP-2009-192554-A propose dividing an interior of the development device with a partition into a supply compartment from which developer is supplied to the developer bearer and a collection compartment to which the developer that has passed through the development range is collected. An edge face of the partition faces the surface of the developer bearer on a cross section perpendicular to the axial direction of the development device. When the supply compartment is divided from the collection compartment, developer having a lower toner concentration that has passed through the development range is not collected in the supply compartment. Accordingly, fluctuations in the image density of toner images formed on the latent image bearer can be limited.
Additionally, in the development devices proposed in JP-2010-197539-A and JP-2009-192554-A, the supply compartment and collection compartment vertically overlap with each other at least partly. This configuration can reduce the lateral size of the development device.